1. Field of the Invention
The present invention relates to a substrate applicable to a circuit board etc., constructed by forming an electroconductive pattern on a glass substrate, and a method for producing the substrate.
2. Related Background Art
There are the following examples conventionally known as substrates in which the electroconductive pattern is formed on the glass substrate, and production methods thereof. As an example, an Ag paste is printed on the glass substrate to form a desired electroconductive pattern and it is baked to be fixed. In another example, a semiconductor layer of ZnO or WO.sub.3 is formed on the glass substrate, thereafter a layer of Pd, Pt, Au, Ag, or the like is deposited thereon by plating, and then an electroconductive layer of Cu or the like is deposited by plating to form the electroconductive pattern (Japanese Laid-open Patent Applications No. 4-17211 and No. 6-61619).
In still another example, an undercoat metal layer of nickel is formed on the glass substrate by electroless plating, thereafter an insulating layer is formed in a predetermined pattern thereon, then a metal layer is deposited over exposed portions of the undercoat metal layer by electroplating of copper, the aforementioned insulating layer is then removed, and exposed portions of the undercoat metal layer of nickel is etched away to form a desired electroconductive pattern (Japanese Laid-Open Patent Application No. 8-227656).
The plated layers on the glass substrate, obtained by the conventional treating methods, had the following problems, however. In the case where the Ag paste is printed on the glass substrate to form the electroconductive pattern, lead glass needs to be added in the paste in order to enhance adhesion to the glass substrate, which increases wire resistance of the electroconductive pattern finally obtained, as compared with bulk Ag. In addition, a heat treatment near 500.degree. C. is necessary for increasing adhesive strength between wires and the substrate, which poses additional problems that the energy cost becomes higher and that warp or strain is more likely to occur in the case wherein the substrate is soda lime glass or the like.
Similarly, in the case wherein the semiconductor layer of ZnO or WO.sub.3 is formed on the glass substrate so as to serve as an undercoat layer, a heat treatment at high temperature is necessary in the film-forming process for forming the semiconductor layer of these materials, and thus warp or strain of the glass substrate is likely to occur.
When only the nickel plated layer formed on the glass substrate by electroless plating is used as an undercoat layer, it obviates the need for baking at high temperature necessary in the printing process, but it does not mean that the heat treatment is unnecessary for the substrate. In the case of this process being used, the heat treatment is also necessitated in order to enhance the adhesive strength at the interface between the glass substrate and the nickel plated layer. The reason is that if the plated layer were formed in the thickness enough for wires on the substrate with omitting this heat treatment the risk of exfoliation would increase due to increase in membrane stress.
When the electroless nickel plated layer is baked, for example, at the temperature of about 150.degree. C.-300.degree. C., there will arise, however, a problem that an oxide film is formed in the surface of the plated layer to degrade adhesion to a deposit film thereafter. If this oxide film is attempted to remove with a chemical, there will often arise a problem that not only the oxide film but also the interface portion between the glass substrate and the nickel plated layer are damaged because of influence of the chemical, so as to degrade the adhesion.